1. Field
One or more embodiments of the present invention relate to a micro-electro mechanical system (MEMS) microphone, and more particularly, to a MEMS microphone that has increased acoustic characteristics by providing a sufficient back-chamber space.
2. Description of the Related Art
A microphone is essentially used in a mobile communication terminal. A conventional condenser microphone includes a diaphragm, a back plate, and a junction gate field effect transistor (JFET). The diaphragm and back plate form a capacitor C of which capacitance changes according to a sound pressure, and the JFET buffers an output signal.
The manufacture of the conventional condenser microphone is formed as a single assembly by bending an edge portion of a case towards a printed circuit substrate after sequentially inserting a vibrating plate (the diaphragm), a spacer ring, an insulating ring, the back plate, a current application ring, and finally the printed circuit substrate on which circuit parts are mounted in the single case.
Recently, a semiconductor processing technique that uses a micromachining technique to which a semiconductor process, in particular, an integration technique is applied has been used as a technique for integrating minute devices on a microphone. This technique that is referred to as a micro-electro mechanical system (MEMS) is used for manufacturing an ultra-small sensor or actuator and an electro-mechanical structure of μm unit.
A MEMS microphone manufactured by using the micromachining technique is manufactured by miniaturizing, increasing the performance, multifunctionalizing, and integrating the conventional microphone parts, such as the vibrating plate, the spacer ring, the insulating ring, the back plate, and the current application ring through a super-precision minute processing. Thus, the stability and reliability of the MEMS microphone may increase.
FIG. 1 is a schematic cross-sectional view of a related-art MEMS microphone 100 having a MEMS chip 120. The MEMS microphone 100 includes a printed circuit substrate 110, the MEMS chip 120 mounted on the printed circuit substrate 110, an application-specific integrated circuit (ASIC) chip 130 that is referred to as an amplifier, and a case 150 having a sound hole 140.
In this configuration, a space formed in the MEMS is referred to as a MEMS inner space 126. In the case of the MEMS microphone 100 in which the sound hole 140 is formed in the case 150, the MEMS inner space 126 is a back chamber. The back chamber is a space for circulating air generated when a vibrating plate vibrates, that is, a space for preventing an acoustic resistance. That is, the space referred to as the back chamber denotes a space located on a side opposite to the side through which an external sound enters with the vibrating plate as a center. As the size of the back chamber increases, the sensitivity and signal to noise ratio (SNR) of the MEMS microphone 100 increase, and thus, the performance of the MEMS microphone 100 increases.
FIG. 2 is a schematic cross-sectional view of another related-art MEMS microphone 102 in which a sound hole 140 is formed in a printed circuit substrate 110 instead of a case 150. No through hole is formed in the case 150. External sound enters through the sound hole 140 formed in the printed circuit substrate 110. In this case, the back chamber is not an inner space of the MEMS microphone 102, but an inner space 151 of the case 150 functions as a back chamber.
In the case of the MEMS microphone 102, since the inner space 151 of the case 150 is the back chamber, the back chamber is quite large. However, in the MEMS microphone 100 of FIG. 1, since the MEMS inner space 126 is the back chamber, the back chamber is very small.
In this case, the SNR of the MEMS microphone 100 is small, and thus, the acoustic quality of the MEMS microphone 100 is reduced.